The invention is in the field of mechanical engineering and specifically relates to the transfer of movements and of torques via flexible shafts.
Flexible shafts of this type allow the transfer of torques for certain applications, for example to points which are difficult to access, e.g. for do-it-yourself (DIY) machinery or for dental applications where machining tools have to be introduced into the mouth of a patient. Small flexible shafts are generally suitable for use in the medical area, for example also for the drive of micropumps such as heart catheter pumps which are introduced into a body for the conveying of the body's own fluids, or for use in micromillers which can be used for removing tissue or deposits.
Various problems are known in the operation of such flexible shafts, in particular at high speeds, with one of these problems comprising the fact that a high noise development can arise due to imbalance or other mechanical irregularities, on the one hand, and also mechanical knocking can arise with high wear resulting therefrom. In addition, a torque has to be transferred which is as high as possible with a low mass of the shaft with a diameter of such flexible shafts which is as small as possible, which is difficult to bring into line with the desire for bending radii which are as tight as possible.
Different proposals are known from the prior art for the further development of such flexible shafts. It can, for example, be seen from the German laying-open publication DE 101 13 208 A1 that with a hollow shaft which is present in the form of a wound resilient coil, individual windings can be omitted to vary the stiffness of the shaft over the length. A better bending capability overall should thereby be achieved and, in addition, irregular rotations and vibrations should be avoided.
A hollow shaft which comprises two spring wire coils wound in opposite senses and can transfer torque in both directions of rotation is generally known from the laying-open publication DE 42 08 221 A1.
A shaft is known from the laying-open publication DE 29 08 143 which is wound from monofil strands and has a constant stiffness over its length.
U.S. Pat. No. 5,108,411 discloses a shaft which is divided into different portions with respect to its length, at least one of said portions having a structure in the manner of a hollow shaft, with a solid shaft portion being connected to the hollow-shaft portion. It is achieved in this manner that the shaft is divided into flexible and less flexible longitudinal portions. The more flexible shaft portions in this respect comprise a coil-type hollow shaft wound with double layers in opposite senses.
A flexible shaft for rotating operation is known from US 2008/0306327 which comprises in order to influence the vibration behavior either different segments arranged in a row after one another, a strand-type element with reinforcement sleeves mounted on the outside or a wound coil having mechanical properties changeable over the length. Reinforcements inserted inwardly into a hollow shaft are also mentioned there.